Patents FR-2 689 231 and FR-2 822 944 disclose methods for assisting in piloting, according to which there is presented, on a display screen of said aircraft, an information presentation which illustrates a vertical plane along a flight path representative of a predetermined flight plan of said aircraft and which comprises:                a system of axes, of which a y-axis is graduated altitude-wise, and an x-axis is graduated distance-wise from the position of the aircraft;        a characteristic symbol representing the aircraft, which is positioned on said y-axis in a position representative of the altitude of said aircraft; and        at least one first trace representing the vertical path of said flight path, and a second trace representing the profile of the ground being flown over.        
Such a known method is above all used in the civilian domain. Furthermore, it relates only to a flight that is made according to a flight plan (along a flight path conforming to said flight plan).
It is known that a civilian flight as performed in the civilian domain has a particular profile (or a series of phases), namely a climb to a maximum cruising altitude (which is sometimes reached via a number of stages), a flight at that altitude, then a descent to the destination altitude. Thus, once the climb has begun, it is continued to the maximum cruising altitude. Similarly, once the descent has begun, it is continued to the destination, and without an intermediate climb being required during this descent.
Such a civilian flight therefore has long climb and descent phases. Generally, the positioning of the abovementioned particular symbol (representing the aircraft) on the y-axis of said system of axes is achieved according to either the selected altitude or the destination altitude.
It will be noted that the present invention is applied more particularly, although not exclusively, to a tactical flight, that is a flight made generally in the military domain and which includes at least one tactical event such as an in-flight refueling, an initially unplanned landing, a jettisoning or a parachuting of troops and/or of equipment, for example. Such a tactical flight has a profile that overall can include several high-altitude flight phases and several low-altitude flight phases. A typical profile of such a tactical flight can, for example, include the following phases: a take-off phase with a climb, a transit to high altitude, a rapid descent to a low-altitude flight zone likely to be dangerous, and in which a tactical event can be performed, such as a jettisoning, for example, then a repeat transit to high altitude, for example to perform an in-flight refueling, and finally a descent to the final destination.
Such a profile therefore includes not only long climb and descent phases, like a civilian profile, but also automatic ground-following paths resulting in short climbs and descents, and including connecting phases between a descent and a flight at low altitude or between a flight at low altitude and a climb.
Because of these latter characteristics, the usual abovementioned information presentation (relating to the vertical plane along the flight plan of the aircraft), which is well suited to a civilian flight, is not totally satisfactory for a tactical flight. In practice, using this usual information presentation as such risks showing up jumps in the position both of the display window and (above all) of said particular symbol representing the aircraft, in transitions from one flight phase to another. Also, with such a usual information presentation, it will be very difficult for the pilot to effectively monitor the future path in all the flight phases likely to be followed by the aircraft.
Furthermore, this usual information presentation is not applicable to a free flight as considered in the present invention, that is, a flight with no flight plan, since this information presentation is produced by definition along a flight path which is representative of the flight plan being followed.